The present invention relates to a vehicular lamp of a type wherein light emitted from a light source bulb is reflected by a reflector to form an outward illuminating light beam. More particularly, the invention relates to such a vehicular lamp in which the reflector is coated with a tinted topcoat layer so as to allow for discrimination from the outer appearance of the vehicular lamp as to whether the lamp is in its ON or OFF state, and for brightening the outward light beam when the lamp is in the ON state.
In a vehicular lamp such as headlamp mounted on an automobile or a two-wheeled vehicle, the technique of reflecting light emitted by a light source bulb with a reflector to form an outward light beam has of course long been well known. In such a lamp, tinting the topcoat layer formed as the outermost layer of the reflecting surface has been conventionally employed both to protect the reflecting surface, which is formed on the upper layer of a lamp body by aluminum deposition, and to change the color of the emitted light.
This technique has been developed based on the phenomenon that when the light emitted from a light source bulb passes through the tinted topcoat layer, light having a specific wavelength is absorbed, so that the color of the reflected light is determined in dependence on the pigment contained in the tinted topcoat layer. Such a lamp is disclosed in Japanese Utility Model Laid-open Publication No. Hei. 2-18202.
According to this technique, for example, if a coating layer containing a blue-based pigment is used as the topcoat layer, in the ON state of the lamp while in use at night, the reddish light emitted by an incandescent bulb can be converted into, for example, white light, similar to the light emitted from a halogen bulb, or white light emitted from a halogen bulb can be converted into the pale blue light typical of a discharge lamp. Therefore, it is possible to facilitate visibility at longer distances and to provide an improved outer appearance for the lamp.
In addition to the above effects obtained when the lamp is in the ON state, in the OFF state during the daytime the tinted topcoat layer of the reflector causes the natural light reflected outward from the lamp chamber to give the lamp a distinctive appearance.
However, in such a lamp a certain portion of the light emitted from the bulb is absorbed due to the passage of the light through the tinted topcoat layer. As a result, the luminous intensity is reduced, causing a problem in light distribution.
If the density of the pigment of the tinted topcoat layer is increased so as to improve the outer appearance of the lamp, the reflection factor of the lamp is decreased, thus further reducing the luminous intensity of the lamp. It has been difficult in the conventional art to satisfy simultaneously the requirements of an improved outer appearance and high luminous efficiency.
FIG. 1 is a vertical sectional view of a vehicular lamp (headlamp) having a reflector provided behind a halogen bulb. The structure of the vehicular lamp 1 will be explained referring to the drawing.
The lamp 1 is formed with generally a cup-like shape. The lamp 1 includes a lamp body 2 with its rear top portion 2a provided with an opening 11 for mounting a light source bulb (halogen bulb) 3, a rubber boot 8 having a predetermined shape for sealing the opening 11, the light source bulb 3 disposed in a lamp chamber 4 inside the lamp body 2, and a front lens 10 mounted so as to close the front opening of the lamp body 2.
The reflector 5 includes a reflecting surface 504 (see FIG. 2) for reflecting bulb-emitted light P1 from the light source bulb 3 forward of the vehicle to form an outward illuminating beam P2. An extension portion (extension reflector) 6 is also provided for covering a gap 7 formed between the reflector 5 and the lamp body 2.
Reference numeral 301 represents a top portion which is painted black for shielding the forward light from the light source bulb 3. In some cases, a shade member (not shown) having the same outer appearance color as that of the reflector 5 may be provided around the light source bulb 3.
In addition to FIG. 1, referring to FIG. 2, which is a partial sectional view of the reflector 5, the structure of the reflector 5 will be explained in detail.
The reflector 5 generally has a four-layer structure including a synthetic resin base body 501 defining the basic shape of the reflector 5, an undercoat layer 502 provided on the upper layer of the base body 501 for smoothing any roughness in the surface of the base body 501, a reflecting surface 504 including a surface formed by an aluminum-deposited layer 503 and provided on an upper layer of the undercoat layer 502, and a topcoat layer 505 for protecting the reflecting surface 504.
The reflector otherwise can be formed as a three-layer structure by omitting the undercoat layer 502.
The reflector 5 has substantially a cup-shaped outer appearance. The reflector 5 is provided with a paraboloidal effective reflector portion (effective reflecting surface) 5x (see FIG. 1) which can effectively contribute to formation of the reflected light P2, and a non-effective reflector portion (non-effective reflecting surface) 5y having an extension wall (flat plate-like surface) extending from the end of the effective reflector portion 5x toward the front lens 10. The non-effective reflector portion 5y does not directly contribute to the formation of the reflected light P2 but is required for structural or design reasons.
Since one of the purposes of the topcoat layer of the reflector 5 is to protect the reflecting surface 504, it is required that the bulb-emitted light P1 pass through the topcoat layer without greatly lowering its luminous intensity, while reflected light (outward emitted light) P2 having a desired light distribution is formed on the reflecting surface 504, i.e., the transparent topcoat layer (not shown).
Recently, it has been proposed to form a transparent topcoat layer by xe2x80x9csmoke coatingxe2x80x9d (also called xe2x80x9ccolor clear coatingxe2x80x9d) wherein a pigment 505a is dispersed in a base medium to form a tinted topcoat layer 505. With this reflected light coloring technique, the reflected light P2 is converted into colored reflected light while reducing the amount by which the luminous intensity of the reflected light P2 is lowered due to coloring.
For carrying out this reflected light coloring technique, there has been proposed a method for forming a five-layered structure wherein smoke coating is performed on an upper layer of a transparent topcoat layer in a separate step. However, since the number of steps is increased with such a technique, a method for combining the topcoat layer with the tinted topcoat layer 505 so as to not increase the number of layers is generally preferred.
With the reflected light coloring technique, by forming the tinted topcoat layer 505 as a blue coated layer, when the lamp is turned ON at night, the light P1 from the light source bulb (halogen bulb) 3 is converted into colored reflected light of a pale blue color or the like, similar to the light from a discharge-type bulb. Also, using this technique the reddish light from an incandescent bulb can be converted into substantially white reflected light, similar to the light from a halogen bulb.
Thus, the reflected light coloring technique has merit in that it prevents a large reduction in the brightness of the light from the lamp 1, preserving visibility over long distances, while enhancing the outward appearance of the lamp, without having to employ an expensive light source.
When the lamp is in the OFF state, due to the provision on the reflector 5 of the tinted topcoat layer 505, light P3 entering from outside the light chamber 4 is tinted. Therefore, the outer design of the lamp 1 can be distinguished in terms of coloration, and the visual recognition ability of the vehicle in the evening can be enhanced.
However, in the conventional reflected light coloring technique, the tinted topcoat layer 506 is formed over the entire reflector 5, i.e., over both the effective reflector portion 5x and the non-effective reflector portion 5y. With this arrangement, although the luminous intensity of the reflected light formed by the effective reflector portion 5x is generally acceptable in terms of overall light distribution, it is lowered somewhat due to the presence of the tinted topcoat layer 505. Therefore, visibility over longer distances is lowered, and the overall quality of the lamp is reduced.
It is an object of the present invention to provide a vehicular lamp which avoids the problem of lowered luminous intensity of outside light reflected by the lamp.
To achieve the above and other objects, the invention provides a vehicular lamp in which light emitted from a light source bulb is reflected by a reflector to form an outward light beam wherein the reflector is formed of a paraboloidal effective reflector portion contributing to formation of the outward-emitted light and a non-effective reflector portion formed as an extension wall to satisfy structural or design requirements but not contributing to the formation of the outward illuminating light beam, and only the non-effective reflector portion is coated with a tinted topcoat layer.
With this structure, in the ON state of the lamp the bulb-emitted light is reflected by the effective reflector portion not coated with a tinted topcoat layer to form the outward beam. Therefore, the problem of reduced light distribution due to a reduction in luminous intensity is avoided, although the reflected light of the outward beam cannot be colored.
In the OFF state of the lamp, tinting is added to the outside reflected light by the non-effective reflector portion provided with the tinted topcoat layer. The design of the vehicular lamp thus can be uniquely distinguished.
In an embodiment of the invention in which the reflector is provided separately from the lamp body and an extension portion is disposed in the vicinity of a front lens for covering a gap formed between the reflector and the lamp body, only the extension portion is provided with a tinted topcoat layer.
In another embodiment where the reflector is provided separately from the lamp body, the reflector is formed of an effective reflector portion contributing to formation of the outward beam and a non-effective reflector portion not contributing to formation of the outward beam, and an extension portion is disposed in the vicinity of the front lens for covering a gap formed between the reflector and the lamp body, and each of the non-effective reflector portion and the extension portion is coated with a tinted topcoat layer. In this case, the entire lamp chamber (the entire inner side of the front lens) appears in a desired color.
The coloration of the reflected light largely depends on the dispersion state of pigments in the tinted topcoat layer, and the dispersion state of the pigments is affected by the particle diameter. Considering the aforementioned facts, the desired coloration of the reflected light is obtained by limiting the particle diameter of the pigments within a certain range. More specfically, the diameter of the pigment particles dispersed in the tinted topcoat layer is preferably in a range from 0.01 to 0.5 xcexcm, more preferably 0.04 to 0.12 xcexcm. By limiting the particle diameter of the pigments within this range, it is possible simultaneously to satisfy the requirements of both coloring and concealment (transparency).
At least one of a phthalocyanine-based pigment and a cobalt-based pigment may be employed. Both phthalocyanine-based pigment and cobalt-based pigment provide vivid coloration as well as excellent weather resistance, heat resistance and corrosion resistance.
The luminous intensity of the reflected light depends on the reflection factor, which in turn depends on the density of the pigment which determines the shielding of the reflecting surface. Since the luminous intensity of the reflected light can be controlled by adjusting the relative amount of pigment, the relative amount of the phthalocyanine-based pigment in the coloring paint used for forming the tinted topcoat layer is preferably set in the range from 0.04 to 0.12 wt %, more preferably 0.05 to 0.10 wt %.
As described above, the present invention is capable of not only solving the problem of a decrease in the luminous intensity of the reflected light (outward beam) that has passed through the tinted topcoat layer, but also causing the reflected light appear to be in a desired color. Therefore, the present invention is significant in providing a vehicular lamp exhibiting good light distribution performance and excellent outer appearance.